When producing turbine blades, the final machining stage of the internal surface of the turbine blade is typically done by means of milling cutting inserts having round cutting edges. In such a case, the total usable sector used to cut by such a cutting insert is usually greater than 120°, therefore, the cutting insert may be indexed only two times since a third indexing would not be able to utilize a full range sector, i.e., a cutting edge spanning more than 120°.
Known round cutting inserts or cutting inserts having round cutting edges are often single sided, and, as mentioned, may fully utilize only two cutting edges. For example, U.S. Pat. No. 4,175,896 discloses a single sided cutting insert having two arcuate cutting edges which are eccentric to each other and separated from each other by diametrically symmetric flat faces.
Round double sided cutting inserts are typically ceramic inserts and are devoid of a central through bore for the passage of a clamping screw. The lack of a through bore is a disadvantage since it requires utilizing a more complex and expensive retaining system.
It is an object of the present invention to provide a double-sided indexable cutting insert having four or more round cutting edges.
It is an object of the present invention to provide a double-sided indexable cutting insert having four round cutting edges wherein each of the cutting edges extends more than 120°.
It is an object of the present invention to provide a tool holder for a double sided cutting insert having four rounded cutting edges and a through bore, the cutting insert being retained within the tool holder by means of a clamping screw that passes through the through bore.